The present invention relates to gaseous fuel engines, and more particularly, to a low pressure fuel system for a gaseous fuel engine.
Large stationary engines used to power pumps, generators and the like are often designed to burn gaseous fuels such as natural gas, butane, propane, methane or other combustibles in a gaseous state. Adequate pressurization of the fuel is necessary for efficient performance of the engine. While some gaseous fuel sources supply gaseous fuel at high pressure, such that introduction of the fuel directly into the intake manifold of the engine is possible, other gaseous fuels are supplied at low pressure. For example, it is known for natural gas suppliers to deliver natural gas at pressures substantially less than the intake manifold pressure of many gaseous fuel engines. If natural gas or other gaseous fuel is supplied at low pressure, the pressure must be raised to a pressure greater than the pressure in the intake manifold, for efficient operation of the gaseous fuel engine.
It is known to use compressors to raise the pressure of a low pressure gaseous fuel, as necessary, to introduce the fuel to the intake manifold. Reciprocating compressors or rotary screw compressors can be used to increase the fuel pressure. However, often, such compressor systems are large and expensive, and may require considerable space for installation and use. Adequate space for a large compressor system, including a screw or rotary compressor and a drive motor, may not be available, readily. Further, operating such compressor systems with independent electric motors can be expensive.
U.S. Pat. No. 5,329,757 discloses a method and system for increasing the pressure of gaseous fuel delivered to the fuel system of a gas turbine engine. Gaseous fuel turbochargers are used to compress the gaseous fuel supplied to the gas turbine engine. Pressurized or compressed air is discharged from a high pressure section of the gas turbine engine, and is communicated to turbines powering a plurality of compressors. Gaseous fuel supplied to the compressors is raised in pressure by the compressors, for subsequent introduction in to the gas turbine engine.
It is known to use turbochargers to provide combustion air to internal combustion engines at higher pressure and density than atmospheric pressure and density. The goal of increasing the gaseous fuel pressure can be achieved using a separate, independent turbocharger system for the gaseous fuel, or by introducing the gaseous fuel with the combustion air at the inlet of the first stage of a single, combined turbocharger system. However, providing a separate, independent gaseous fuel turbocharger, or introducing even low pressure gaseous fuel along with combustion air at the inlet for the first stage of a combined combustion air and gaseous fuel turbocharger requires additional work of the compressor in compressing the fuel.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, a fuel system for a gaseous fuel internal combustion engine is provided with a source of compressed gaseous fuel and a turbocharger including a first compressor having a first compressor wheel, a first inlet and a first outlet each associated with the first compressor wheel; and a second compressor having a second compressor wheel, a second inlet and a second outlet each associated with the second compressor wheel. An interstage duct interconnects in fluid flow communication the first outlet of the first compressor wheel with the second inlet of the second compressor wheel. A gaseous fuel conduit is disposed between and interconnects, in fluid flow communication, the source of compressed gaseous fuel and the interstage duct.
Another aspect of the invention is a method of operating a gaseous fuel system for an internal combustion engine, with steps of providing a multi-stage compressor including a first compressor having a first compressor wheel, a first inlet associated with the first compressor wheel, and a first outlet associated with the first compressor wheel; and a second compressor having a second compressor wheel, a second inlet associated with the second compressor wheel, and a second outlet associated with the second compressor wheel; fluidly interconnecting in series the first outlet of the first compressor with the second inlet of the second compressor using an interstage duct; providing a source of low pressure gaseous fuel; and conducting gaseous fuel from the source of low pressure gaseous fuel to the interstage duct.